Electron gun device for color tube

ABSTRACT

An electron gun device for color television picture tubes. The electron gun has three cathodes and a plurality of grids. Means are provided for equalizing the cutoff voltages of the cathodes by equalizing the intensity of the electric field reaching the cathodes from the grids. Equalization preferably is obtained by making one or more of the apertures in the first and second grids of a diameter different from that of the other apertures, or by making the distances of one or more of the cathodes from the grids different from the corresponding distances of the other cathodes, or by a combination of both of these arrangements.

waited States Patent 1191 Ueno et al. Aug. 28, 1973 [5 ELECTRON GUN DEVICE FOR COLOR 2,861,208 11/1958 Benway 313/70 c TUBE 2,887,598 5/1959 Benway 313/70 c 2,957,l06 lO/l960 Moodey 3l3/70 C X [75] Inventors: Kiichi Ueno; Senri Miyaoka, both of 4, 9 2 19 6 v n Hekken, 313 70 0 Kanagawa-ken, Japan 3,448,316 6/1969 Yoshida et al 313/69 [73] Assignee: Sony Corporation, Tokyo, Japan Primary Examiner-Robert Sega] [22] F'led: 1969 Attorney-Albert C. Johnston, Robert E. lsner, Lewis 211 App] 315,941 H. Eslinger and Alvin Sinderbrand [30] Foreign Application Priority Data [57] ABSTRACT Apr. 14, 1968 Japan 43/24589 An electron gun device for color television picture Apr. 14, 1968 Japan 43/24590 tubes The electron gun has three cathodes and a rality of grids. Means are provided for equalizing the [52] US. Cl. ?l3/70 C, 315/82 R cutoff voltages of the cathodes by equalizing the imam [51 1 'f H011 29/50 H01] 31/20 sity of the electric field reaching the cathodes from the [58] Fleld of Search, 313/69 C, 70 C, 70 grids. Equalization preferably is obtained y making one or more of the apertures in the first and second References Clted grids of a diameter different from that of the other ap- UNITED STATES PATENTS ertures, or by making the distances of one or more of 2,726,347 12 1955 Benway 313/70 c the at d s fr m th grids different from the corre- 2,735,031 2/1956 Woodbridge.... 313/70 C sponding distances of the other cathodes, or by a com- 2,825,845 3/1958 Jonker et a1. 313/70 C X bination of both of these arrangements. 2,825,847 3/1958 De Gier 313/70 C X 2,850,658 9/1958 Allwine.... 313/70 C 3 Claims, 9 Drawing Figures 27? i y I T 2 ,i /F dz/z L i 2 T" r 8 d 1 8 l8 2 I d .11. .i

1 2 L I i 2/ ,P zz Z5 PATENTED M1928 ms SHEEI 1 [If 2 1 ELECTRON GUN DEVICE FOR COLOR TUBE This invention relates to an electron gun device, and particularly to an electron gun device for a single-gun, plural-beam type of color television picture tube.

In certain prior color picture tubes having multiple cathodes, the cutoff voltages of the cathodes are not equal to one another. The result of this imbalance is that the gamma characteristics of the three colors in the picture produced by the tube are difierent and the colors are not natural.

in view of the foregoing, a major object of this invention is to provide a plural-cathode electron gun device whose cathodes have the same cutoff voltages. A further object of the invention is to provide a relatively simple and inexpensive means for equalizing the cutoff voltages of such cathodes.

In accordance with the present invention, the foregoing objects are met by the provision of means for equalizing the cathode cutoff voltages by equalizing the intensity of the electric field reaching the cathodes from the grids of the electron gun. The equalization means selectively limits the amount of flux reaching one or more of the cathodes. In the preferred embodiment of the invention, equalization is accomplished by making one or more of the apertures in the first and second grids of a diameter difi'erent from that of the other apertures, or by making the distances of one or more of the cathodes from the grids different from the corresponding distances of the other cathodes, or by a combination of both of these arrangements.

Further objects and advantages of the invention will be pointed out or made apparent in the following description and drawings.

In the drawings:

FIG. 1 shows a typical color television picture tube in which the electron gun of this invention can be used;

FIG. 2 is an enlarged, broken-away partially schematic view of a portion of the electron gun shown in FIG. 1;

FIGS. 3A, 3B, 4A, 4B and 4C are views similar to that of FIG. 2, each showing a different embodiment of the invention;

FIG. 5 is an enlarged detailed view of the preferred embodiment of the invention; and

FIG. 6 is a graph illustrating certain performance characteristics of the electron gun of the present invention.

FIG. 1 of the drawings shows a single-gun, pluralbeam color picture tube 10 which is described in detail in U. S. Pat. application Ser. No. 697,414, filed on Jan. 12, 1968, and assigned to the same assignee as this application. The color picture tube 10, which is known by the name Trinitron, includes a glass envelope 11 (indicated in broken lines) having a neck 12 and cone 13 extending from the neck to a color screen S provided with the usual arrays of color phosphors S S and S and with an apertured beam-selecting grid or shadow mask 6;. Disposed within the neck 12 is an electron gun A having cathodes K K and K each of which is a beam-generating source with its thermal electronemitting surface disposed as shown in a plane which is substantially perpendicular to the longitudinal axis of the electron gun A. In the embodiment shown, the beam-generating surfaces are arranged in a straight line so that the respective beams B B and B emitted therefrom are directed in substantially horizontal planes, with the alignment of the central beam B being coincident with the axis of the gun.

A first grid G, is spaced from the beam-generating surfaces of cathodes K K and K3 and has apertures g g,,;, and g formed therein in alignment with the respective cathode beam-generating surfaces. A common grid 6: is spaced from the first grid G, and has apertures g g and 3 formed therein in alignment with the respective apertures of the first grid 6,. Successively arranged in the axial direction away from the common grid G are open-ended, tubular grids or electrodes G,,, G, and G respectively, with cathodes K K and K grids G, and G and electrodes 6,, G, and 0,, being maintained in the assembled positions shown in the drawings by means of suitable non-illustrated support means of an insulating material.

For operation of the electron gun A of FIG. 1, appropriate voltages are applied to the grids G, and G, and to the electrodes 6,, G. and 6,. Thus, for example, a voltage of O to minus 400V is applied to the grid G,, a voltage of 0 to 500V is applied to the grid 6,, a voltage of 13 to ZOKV is applied to the electrodes G and G and a voltage of 0 to 400V is applied to the electrode 0,, with all of these voltages being based upon the cathode voltage as a reference. As a result, the voltage distributions between the respective electrodes and cathodes, and the respective lengths and diameters thereof, may be substantially identical with those of a unipotential-single beam type of electron gun which has a single cathode and first and second single-apertured grids.

With the applied voltage distribution as described hereinabove, an electron lens field will be established between grid G and the electrode G to form an auxiliary lens L as indicated in dashed lines, and an electron lens field will be established around the axis of electrode G.,, by the electrodes 6,, G, and G to form a main lens L, again as indicated in dashed lines. In a typical use of electron gun A, bias voltages of V are applied to the cathodes K K and K and bias voltages of 0V, 300V, 20KV, 200V and ZOKV may be applied, respectively, to the first and second grids G, and G and the electrodes 6,, G, and G Further included in the electron gun A of FIG. 1 are electron beam convergence deflecting means F which comprise shielding plates P and P disposed in the depicted spaced relationship at opposite sides of the gun axis, and axially extending deflector plates Q and O which are disposed, as shown, in outwardly-spaced, opposed relationship to shielding plates P and P, respectively. Although depicted as substantially straight, it is to be understood that the deflector plates Q and Q may, alternatively, be somewhat curved or outwardly bowed, as is well known in the art.

The shielding plates P and P are equally charged and disposed so that the central electron beam B will pass substantially undeflected between the shielding plates P and P, while the deflector plates Q and Q have negative charges with respect to the plates P and P so that respective electron beams B and 8,, will be convergently deflected as shown by the respective passages thereof between the plates P and Q. More specifically, a voltage V which is equal to the voltage applied to the electrode G may be applied to both shielding plates P and P, and a voltage V,,, which is some 200 to 300V lower than the voltage V is applied to the respective deflector plates Q and Q to result in the respective shielding plates P and P being at the same potentiai, and to result in the application of a deflecting voltage difference or convergence deflecting voltages V between the respective plates P and Q and P and Q and it is, of course, this convergence deflecting voltage V which will impart the requisite convergent deflection to the respective electron beams B and B,,.

In operation, the respective electron beams B B and 8,, which emanate from the beam generating surfaces of the cathodes K K and K will pass through the respective grid apertures g g and g,,,, to be intensity modulated with what may be termed the red," green and blue intensity modulation signals applied between the said cathodes and the first grid 6,. The respective electron beams will then pass through the common auxiliary lens L to cross each other at the center of the main lens L. Thereafter, the central electron beam B,; will pass substantially undeflected between shielding plates P and P since the latter are at the same potential. Passage of the electron beam 8,, between the plates P and Q and of the electron beam 8,, between the plates P and Q will, however, result in the convergent deflections thereof as a result of the convergence deflecting voltage V applied therebetween, and the system of FIG. 1 is so arranged that the electron beams B B and B will desirably converge or cross each other at a common spot centered in an aperture between adjacent grid wires g of the beam selecting grid or mask G so as to diverge therefrom to strike the respective color phosphors of a corresponding array thereof on screen S. More specifically, it may be noted that the color phosphor screen S is composed of a large plurality of sets or arrays of vertically extending red, green and blue phosphor stripes or dots S 5 and S with each of the arrays or sets of color phosphors forming a color picture element as in a chromatron type color picture tube. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly fonned color picture elements.

The voltage V may also be applied to the lens electrodes G and G and to the screen S as an anode voltage in conventional manner through a non-illustrated graphite layer which is provided on the inner surface of cone 13 of the tube envelope. The grid wires of screen grid G may have a post-focusing voltage V ranging, for example, from 6 to 7KV applied thereto as indicated.

To summarize the operation of the depicted color picture tube of FIG. 1, the respective electron beams B B and B, will be converged at screen grid G and will diverge therefrom in such manner that electron beam B wll strike the blue phosphor S electron beam B will strike the green" phosphor S and electron beam B will strike the red phosphor S of the array or set corresponding to the grid aperture at which the beams converge. Electron beam scanning of the face of the color phosphor screen is effected in conventional manner, for example, by horizontal and vertical deflection yoke means indicated in broken lines at D and which receives horizontal and vertical sweep signals whereby a color picture will be provided on the color screen. Since, with this arrangement, the respective electron beams are each passed, for focusing, through the center of the main lens L of the electron gun A, the beam spots formed by impingement of the beams on the color phosphor screen 8 will be substantially free from the effects of coma and/or astigmatism of the said main lens, whereby improved color picture resolution will be provided.

FIG. 2, which is an enlarged view of the cathode region of the tube 10 shown in FIG. 1, shows thermal electron emitting surfaces 14, 15 and 16 of three cathodes K K and K which are arranged in a plane 21 which is perpendicular to the longitudinal axis of the tube. The first grid G, is arranged in a similarly perpendicular plane 22 which is located at a distance D, from the plane 21. The three circular apertures g g and g,,, of grid G, have equal diameters 42, and (35, The second grid G, is arranged in another similarly perpendicular plane 23 which is located at a distance D: from the plane 22. The three apertures g g and g of grid 6, have equal diameters di da and Applicants have discovered that when a high voltage is applied to the third grid 6,, the intensity of the electric field reaching the center cathode K is greater than the intensity of the electric field reaching the other cathodes on both sides, and that the cutoff voltage (absolute value) of the cathode K is greater than the cutoff voltages of the other cathodes K and K,,. This difference in cutoff voltages causes the problems set forth hereinabove. That is, although the video signal voltages applied to the cathodes K K and K may be selected to have the same voltages to produce a white picture, because of the cutoff voltage imbalance, the video signal voltages must be changed with respect to each other according to the differences in their cutoff voltages.

Two arrangements are shown in FIGS. 3A and 3B for providing the same cutoff characteristics for the cathodes K K and K The arrangement shown in FIG. 3A, the electric field reaching the cathode K through the aperture g is reduced by selecting the diameter Q5"; of the central aperture g in the first grid G, to be smaller than the diameters and da of the other apertures g and g in the first grid.

The arrangement of FIG. 3B is like that of FIG. 3A except that the diameter d2 of the central aperture g of the second grid G, also is smaller than the diameter of its neighboring apertures.

Other arrangements for the same purpose are shown in FIGS. 4A, 4B and 4C. In each of these arrangements, the diameters of the apertures in grids G, and G are uniform, but the distances D, and/or D relating to the central electron beam (green) is made greater than the corresponding distances for the other electron beams (blue and red) in order to equalize the intensity of the electric field reaching each cathode.

In the FIG. 4A arrangement, the intensity of the electric field reaching the central cathode K is reduced by locating the beam-emitting surface 15 of that cathode farther away from grids G, and G than the other cathodes by a distance D,. Of course, this has the effect of locating cathode K at a greater distance from the control electrode G,,.

In the FIG. 4B arrangement, the same effect is achieved by bending the metal plate forming grid G, away from grid G, by a distance D, in the vicinity of the central aperture g In the FIG. 4C arrangement, the structural features shown in FIGS. 4A and 48 have been combined to give an even greater reduction in the electric field intensity at the surface 15 of cathode K FIG. 5 shows one specific example of the gun device described in the foregoing description. The material of which the grids G G and G are formed is stainless steel of 0.2 mm. thickness. Other dimensions and the voltages applied to the grids are shown in FIG. 5. It can be seen that the FIG. 3A arrangement is used in the FIG. 5 structure; that is, the diameter 4m; is 0.77 mm, and d is greater, 0.8 mm.

FIG. 6 shows experimentally observed relationships between various voltages observed in the structure shown in FIG. 5. In FIG. 6:

Ekco is the cutoff voltage between the cathode K and the first grid 0,; that is, the negative voltage necessary to be applied to G to cause cathode cutoff;

Ec is the voltage applied to the second grid G The cutoff characteristics of the side beams are shown as line A in FIG. 6. Line 13 represents the cutoff characteristic of a structure like the FIG. 5 structure except that both 4m; and qb are equal to 0.8 mm; that is, a structure in which the diameters of the center apertures of the first and second grids G, and G are equal to diameters of the corresponding side apertures. It is seen from FIG. 6 that there is a difference of about eight volts between the cutoff characteristic curves A and B throughout the section labeled operating range.

In the gun device actually shown in FIG. 5; that is, one having a center aperture of the first grid G whose diameter dm; is smaller than the diameter of its neighboring apertures, the cutoff characteristics of the center beam are shown as Line C. The differences between the cutoff voltages of the center beam and the side beams are so small as to be negligible in the operation range." Thus, the problem of differing cathode cutoff voltages has been solved.

In each of the embodiments of this invention, the relative reduction in the diameter of the apcrgure g and/or the aperture g (FIGS. 3A and 3B), or the increase of the distance from the beam generating surface 15 of the central cathode K to the portion of grid G having the corresponding aperture g and/or to the portion of the grid G having the corresponding aperture g serves to relatively decrease the angle of the cone that can be projected from the peripheries of the apertures to the center of the beam generating surface 15. Thus, although the electric field constituting the auxiliary lens L (FIG. 1) is most intense at the axis of the gun, the effect of that field at surface 15 of central cathode K is minimized so as to be equalized with the effect of the field at surfaces 14 and 16 of side cathodes KB and KB.

The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth in the claims.

We claim:

1. An electron gun device for a color picture tube comprising two side cathodes and a central cathode therebetween having beam generating surfaces arranged substantially in a row for emitting electrons generally in parallel directions, first and second grids spaced successively in the axial direction away from said beam generating surfaces and having apertures respectively aligned with the beam generating surfaces and through which the emitted electrons are collimated into respective electron beams, and a plurality of electrodes maintained at different potentials and arranged axially following said second grid to provide an electric field defining a main lens means by which said beams are focused and cooperating with said second grid to provide another electric field defining an auxiliary lens means by which the beams from said side cathodes are converged with respect to the beam from said central cathode for passage of all of the beams through the center of said main lens means, the angle of a cone that can be projected to the center of said beam generating surface of said central cathode from the peripheries of the respective aligned apertures of said grids being smaller than the angles of the corresponding cones for said side cathodes for equlizing the effects of said other electric field at said beam generating surfaces of said cathodes so that the latter will have equal cutoff voltages.

2. An electron gun according to claim 1, in which at least one of the apertures of said first and second grids which are aligned with said central cathode is of a size smaller than the sizes of the apertures of said grid aligned with said side cathodes.

3. An electron gun according to claim 1, in which said beam generating surface of the central cathode is at a distance from the aligned aperture in at least one of said first and second grids that is greater than the dis: tance from the beam generating surfaces of said side cathodes to the corresponding apertures of the grids.

s s a a s 

1. An electron gun device for a color picture tube comprising two side cathodes and a central cathode therebetween having beam generating surfaces arranged substantially in a row for emitting electrons generally in parallel directions, first and second grids spaced successively in the axial direction away from said beam generating surfaces and having apertures respectively aligned with the beam generating surfaces and through which the emitted electrons are collimated into respective electron beams, and a plurality of electrodes maintained at different potentials and arranged axially following said second grid to provide an electric field defining a main lens means by which said beams are focused and cooperating with said second grid to provide another electric field defining an auxiliary lens means by which the beams from said side cathodes are converged with respect to the beam from said central cathode for passage of all of the beams through the center of said main lens means, the angle of a cone that can be projected to the center of said beam generating surface of said central cathode from the peripheries of the respective aligned apertures of said grids being smaller than the angles of the corresponding cones for said side cathodes for equlizing the effects of said other electric field at said beam generating surfaces of said cathodes so that the latter will have equal cutoff voltages.
 2. An electron gun according to claim 1, in which at least one of the apertures of said first and second grids which are aligned with said central cathode is of a size smaller than the sizes of the apertures of said grid aligned with said side cathodes.
 3. An electron gun according to claim 1, in which said beam generating surface of the central cathode is at a distance from the aligned aperture in at least one of said first and second grids that is greater than the distance from the beam generating surfaces of said side cathodes to the corresponding apertures of the grids. 